Many species of commonly used wood such as pine, hemlock and the like have relatively poor resistance to stain and decay caused by various forms of common fungi. Thus untreated products, e.g., non-kiln dried products, such as lumber, poles, posts and like made from these woods may have a limited useful life when stored or utilized in a moist environment where contact with fungi can be expected. For example, the growth of fungus on wet raw wood material of a fungi susceptible species oftentimes occurs within two or three weeks after initial exposure to a warm, moist environment. Fungal growth typically manifests itself initially as an objectionable stain on the surface of the wood material and such growth can, over an extended period of time, cause decay and destruction of the wood material.
It has been a fairly common practice in the lumber industry to treat such fungi susceptible wood products with various chemical agents to impart fungi-induced stain and rot resistance to the products. The most widely used agents in recent years have included chlorophenols such as pentachlorophenol and copper chromium arsenates. While these agents in most instances provide sufficient protection for the treated wood products, adverse health and environmental risks are posed by the use of these chemicals.
It has been recognized for some time that certain species of wood such as various species of cedar wood are significantly more resistant to stain and decay caused by fungi then other species of wood. This characteristic of these species of wood has been attributed to their relatively high content of .alpha., .gamma., and B-thujaplicin, B-dolabrin, B-thujaplicinol, thujic acid and methyl thujate, the thujaplicins being the primary constituent and are recognized as the primary agents responsible for decay resistance. The sum total of these chemicals may be quantified as "thujaplicin equivalents".
U.S. Pat. No. 4,413,023 to Chow, issued on Nov. 1, 1983, discloses a method of treating wood to prevent stain and decay which includes extracting from a decay resistant species of wood material fungi growth inhibiting material and wetting the surface of wood to be treated with a solution of the extracted material. It is further taught in this patent that the extraction of the fungi growth inhibiting material from the decay resistant species of wood material is accomplished by immersing the wood material in an extracting solvent for a period of time ranging from four to twenty-four hours and then decanting the solution for use in treating wood material. A significant drawback of this extraction is that the solutions obtained are relatively weak in concentration of the fungi growth inhibiting material and thus wood material treated with the solutions may be protected from fungal growth for a limited time period, generally less than about one year, sometimes six months or less.